The disadvantage was that the removal needed to be done in conjunction with the in-place Portland cement base. “One of the project requirements was no open cuts or drop-offs would be tolerated during construction, overnight and weekends,” says Polak.
The other consideration was the 48 water valve covers and 28 manholes. “The utilities needed to be removed before construction,” says Polak. “The mill could traverse the utilities, but the low profile of the paver and height of the screed would not be able to go over or around them.”
All of the utilities where removed before the major construction took place. Steel plates had been placed over the area of the utilities so no debris would enter storm or sanitary sewers and water valves would not get clogged with fines from the operation.
Another challenge was the areas that showed deeper lying issues that needed to be repaired prior to operation. These areas were cut to a depth where the base became solid. Stone was placed to grade and compacted, and then 2 inches of hot mix binder course was placed and compacted to keep the aggregates in the patches stable.
E.J. Breneman used a Wirtgen milling machine with a 2-foot cutting head to excavate along the concrete gutter pans to a depth of 10 inches immediately in front of the in-place Portland cement train. This material was exported from the project site and placed in a recycling center for future use.
As the gutter pans where exposed, the next part of the construction practice was applying the additive. E.J. Breneman used a Stoltz spreader to place its additives.
Determining the additive
Before the project started, a geo-technical engineer was hired by E.J. Breneman. Materials at the depth of re-construction in several areas had been taken from Canvasback Road.
“When taking samples for FDR, it’s important that the section of sampling represents the total depth of the operation that will follow,” says Polak. “If it’s deemed the depth of reclamation is 10 inches, then the sample taken should also be at that depth. The sample should include a representation of all the materials from the asphalt down through the aggregate to the soils in the subbase.”
The entire section was tested and, once analyzed, the geo-technical engineer tested for a compatible additive or combination of additives to add to the combined material at different percentages. Different additives can offer differing strengths, dry and lower moisture contents, or modify soils.
It was determined Portland cement was the correct additive for Canvasback Road. Different percentages of Portland cement were mixed with the additive, broken after curing at different intervals of time such as 7, 14 and 28 days. “This will give different strengths of the materials and guide Kercher Engineering to establish what strengths Canvasback Road would need,” says Polak.
Kercher would take into consideration the ADT (average daily traffic), what type of traffic, ESALs and loading. They may also take into account any future development that might impact the roadway in years to come.
Applying the additive
Once the Geo-tech report was given to the engineer, he then established a mix formula for the project, normally what PSI (pounds per square inch) is required on the entire roadway. Based on the report, the contractor then calibrated its dry bulk spreaders to spread the required Portland cement evenly to mix and produce a compacted base material that will in the prescribed time yield the correct PSI.
“The geo-tech was represented on the project at all times there is mixing and placement underway,” says Polak. “One of his duties is to check moisture in the mixed materials, take mixed samples and produce cores in the laboratory for testing. The geo-tech had a nuclear gauge with him during the period of time mixing was taking place.”
Once the material was placed by the paver, it was compacted. As the process progressed along both gutter pans, the paver left the new mixed material flush with the top of the gutter pan.
Then under compaction, the material compacted down and left a 2.5-inch reveal below the top of the gutter pan. This allowed for the 2.5-inch HMA, which would need to fit flush with the top of the gutter pan.